Foresight Update 31

page 2

Track
Two: Molecular Electronics,
More Probes, and More

by Jim Lewis

Molecular Electronics

Molecular electronics was a major theme of this conference.
Many speakers expressed great optimism that recent technical
progress will lead to practical molecular electronic devices in
the relatively near future  prior to the advent of a mature
molecular manufacturing technology. James Ellenbogen
of MITRE Corporation gave an overview of nanocomputers and
molecular electronics, "Technologies
and Designs for Nanometer-Scale Electronic Computers: A Review
and Prospectus." Two major reviews that largely cover
his talk are
available in Adobe Acrobat (pdf) format. After reviewing the
field, Ellenbogen proposed concepts for a 6 x 6 nm OR gate and a
12 x 12 nm adder carry unit that he intends to build and test in
the coming year.

Much work reported at the conference focused on electronic
properties of fullerene nanotubes. Other work aimed towards
near-term implementation of molecular electronics targeted
polymers with linked aromatic rings. Jerry Darsey
of the University of Arkansas presented the results of
calculations that show certain organic polymers, in the presence
of a magnetic field and when stimulated by appropriate radiation,
generate electric currents that could be used for logic circuits
("Molecular
Dynamics and Ab Initio SCF-MO Modeling of Nanogenerator
and Nanologic Circuit Molecules"). Because different
molecular components could be stimulated by different frequencies
of radiation, the possibility exists to build circuits around
multiple value as well as binary logic.

Scanning Probe Microscope-Based Devices and Approaches

Ulrich Quaade of the Technical University of
Denmark presented work on a single atom switch flipped using an
STM, in ultra high vaccum at room temperature ("Single
Atom Switch on Silicon: Results and Prospects"). He
showed STM images of a dangling bond on a hydrogen-terminated Si
(100) surface jumping back and forth between neighboring Si atoms
in response to a voltage bias applied by the STM tip. The tip is
held far enough from the surface that no chemical reaction
occurs. Such switching could form the basis of a (very slow)
memory unit storing 1013 bits mm-2.

John Michelsen of Zyvex, a recently formed
company with the goal of building an assembler, proposed
strategies for adapting the crude "pick and place"
capabilities of current scanning probe microscopes to the problem
of constructing atomically precise structures with moving parts ("Assembler
Construction by Proximal Probe"). Michelsen noted that
several researchers have already demonstrated placing small
numbers of germanium (Ge) or silicon (Si) atoms on Ge or Si
surfaces by using applied electric fields to transfer the atoms
from a surface to a tungsten (W) tip and then back to the surface
at a chosen location. Such atom placements are insufficiently
precise for mechanosynthesis because the energy required to rip
the atom from the surface is far greater than the energy barrier
to diffusion of the atom around the STM tip. Michelsen proposed
that Si atoms deposited on a gold surface could be picked off by
a W tip and deposited precisely on a Si surface, using favorable
chemical reactions at each step rather than energy introduced by
a voltage pulse.

Michelsen also considered the special problems in fabricating
atomically precise moveable components, in which there is little
room between the opposing surfaces to use scaffolding to hold the
surfaces apart during construction. His proposed solution uses
small groups of atoms (joiners) weakly bonded to the opposed
surfaces. In his example, dimers of Si or sulfur are used at the
top edges of a hydrogen-terminated diamond slider sitting in a
hydrogen-terminated diamond channel to hold the slider in the
channel. As additional layers of diamond are added to the top of
the slider, the joiners are alternately removed from one side of
the slider, reattached at the new upper layer, and then removed
and reattached on the other side. Thus as the slider is built up,
the joiners remain accessible at the upper edge and hold the
opposing surfaces apart. In another strategy to create opposing
nonbonded interfaces, Michelsen proposed using a deposition tool
tall enough to reach into a channel on the opposing surface and
build outward from the channel wall a structure perpendicular to
that wall and extending parallel to and between the first two
surfaces. Using such proposals to begin to bridge the gap between
theory and experiment, Michelsen hopes to use the limited
positioning capabilities of current scanning probes to build
articulated components for first generation diamondoid
assemblers.

Tilman Schaeffer of UC Santa Barbara reported
progress in improving the accuracy of AFM's through making
smaller cantilevers ("Atomic
Force Microscopes for the Study of Protein Motion"). The
10 micron-long cantilevers he used were made of aluminum (to have
a soft enough spring constant) and had a resonance frequency up
to 2.5 MHz, making them much less sensitive to thermal noise than
are conventional cantilevers. An important technical challenge in
making these small cantilevers was redesigning the optical system
that follows the motion of the cantilever as it scans the sample.

Biologically-Based Molecular Switches and Devices

Andrew Mendelsohn of Harvard Medical School
showed how living cells could be designed that register logical
states ("Intracellular
Protein Technology"). He reported an extension of the
protein interaction trap system in yeast cells, a genetic assay
originally developed to determine whether or not two proteins
physically associate within a given cell. If the proteins
interact, a "reporter gene" is activated, ultimately
producing a macroscopic signal from the billions of protein
molecules in a colony of millions of cells that grow from the
initial cell. An important aspect of this technology is the
ability to create fusion proteins, in which a functional domain
from one protein and an unrelated functional domain from another
protein are fused genetically to create one protein with both
functions.

The new development was the creation of cells that signal more
complex relationships among proteins and peptides than the simple
association of two proteins, allowing the representation of
symbolic logic relationships. Cells were created that allowed
simultaneous selection both for and against two distinct
protein-protein interactions, using two distinct reporter genes
to register the variety of interactions possible. Specifically, a
"prey" protein could interact with either, both, or
neither of two "bait" proteins. It was possible to use
such cells to identify peptides that would interact with a given
protein, but not with variants of that protein produced by
mutation. Moreover, one of the protein domains used cycles
between two conformation states with different protein
association properties. Mendelsohn suggested that similarly
designed cells could be used with a large variety of peptides to
produce massively parallel processors for computation. Such
computers would, however, be very slow as reading the reporter
gene ouput usually takes hours.

Steven Smith of City of Hope, Medical Center
described a novel technology ("Uracil
as an Alternative to 5-Fluorocytosine in Addressable Protein
Targeting") for covalently attaching functional proteins
to specific sites on a DNA backbone [see the Recent Progress
column in Update 29]. Because the protein is bound
to the DNA by multiple contacts, the protein is locked tightly in
a specific orientation on the DNA. Smith proposed several devices
that could be constructed using such macromolecular arrays. The
array could be used to position enzymes in space so that the
product of one would be the substrate of another, thus
constituting molecular assembly lines. Proteins could be spaced
at specific distances and angular rotations along a DNA helix to
form a cam shaft.

Perhaps of most interest, molecular switches could be made
using DNA with a long helical hairpin in one strand of the helix
to form a Y-shaped structure. Three proteins, each of which binds
a distinct peptide, could be attached, one to each end of the Y.
In the presence of bifunctional peptides (each containing two of
the three peptide ligands) two proteins, and thus those two ends
of the Y, would be joined. Chromophores could be attached to each
arm of the Y such that changes in the light absorption properties
of the complex, resulting from changes in the distances among the
chromophores, would signal which two arms had been linked.

Claudio Nicolini of the El.B.A. Foundation
described a technique to use an electric field to order
bacteriorhodopsin membrane fragments in a monolayer that was able
to transduce light into electric current ("Towards
a Bacteriorhodopsin-based Light-Addressable Transducer ").
Such devices should be scalable to as small as 2 nm. Nicolini
indicated, however, that actual commercialization would probably
be done with proprietary techniques using octopus rhodopsin,
which has the advantage that it can be separated from the
membrane lipids without denaturing.

Institutions, Markets, and Nanotechnology

Neil Jacobstein of Teknowledge Corporation
focused on business strategies to develop a molecular
manufacturing industry ("R&D
Targets and Regulatory Risks in Molecular Manufacturing").
Beginning with current barriers to the development of molecular
manufacturing, such as a lack of public understanding of science
and technology, a failure to grasp how a "Grand
Challenge" can drive R&D, and a fixation with near term
rewards, Jacobstein proposed possible ways forward that would not
require large government investments in R&D. Pointing to
current work that Apple Computer is doing on an "Educational Object
Economy", he suggested a Web-based Molecular Objects
Economy, in which tools and molecular designs could be made
available on the Web, in open formats, with a variety of open or
closed licensing arrangements possible.

To help guide R&D, he suggested concurrent engineering now
to tackle logistic and support problems associated with complete
molecular manufacturing systems (rather than waiting until after
an assembler is developed before considering such issues), and
focusing on incremental, near term products to create a
"demand-pull" for the further development of the
technology (rather than focusing solely on technology development
and hoping for "spin-off" products).

Finally, as an example of proactively managing risks that
might short-circuit the development of molecular manufacturing,
Jacobstein proposed an international ban on the development of
nano-weapons, beginning with a Web-based dialog on the issues
involved. Pointing out that such bans are most effective if
initiated before the development of the enabling technology, he
put forth the example of the very effective ban on space-based
weapons put into place before the technology to deploy such
weapons was available.

Tanya Sienko described support for
nanotechnology research in Japan ("Present
Status of Japanese Nanotechnology Efforts"), and
reported major Japanese interest in tabletop micromachine
factories as a new paradigm in manufacturing, intermediate
between conventional manufacturing and molecular manufacturing.
As for effort in molecular manufacturing, the Japanese seem to be
watching developments in the U.S. before committing their
resouces in that direction. [American work on table top
micromachine factories was represented at the poster session by Massood
Tabib-Azar of Case Western Reserve University ("Silicon
Wafer-Scale Micro-Fabrication Factory Using Scanning Probe
Micro-Robots")]

Stephen Gillett of the University of Nevada
proposed an approach to developing nanotechnology based upon
complex structures made of silicates rather than of carbon ("Notes
on a Molecular Nanotechnology of Silicates"). After
describing the favorable properties of silicon-oxygen bonds and
noting that silicates, unlike carbon structures, are not
flammable in oxygen and are very abundant on earth and elsewhere,
he proposed that a silicate-based nanotechnology also offered
substantial advantages in terms of near term economic value that
could be created by incremental improvements in current
technology. Noting that zeolite catalysts (silicate minerals
containing voids that very selectively admit some molecules) are
economically important, but are currently limited in their
applications by the small variety of void sizes and shapes
available, Gillett proposed that modest investments in creating
novel silicate structures would bring substantial economic
rewards.

Novel Computing Paradigms for Nanotechnology

Two speakers considered computer science issues related to
nanocomputers and molecular manufacturing. Michael Frank
of the Massachusetts Institute of Technology presented a detailed
analysis showing that the greatest computational efficiency
consistent with the fundamental laws of physics is achieved,
independent of the specific technology used to implement the
nanocomputer, with an architecture that is a three-dimensional
mesh of reversible processors ("Ultimate
Theoretical Models of Nanocomputers"). This is because
the second law of thermodynamics states that entropy cannot be
destroyed, and traditional models of computation are based upon
logically irreversible processors that produce a minimum amount
of entropy with each computation. Identifying the ideal
architecture permits work now to develop device-independent
algorithms based upon that architecture, prior to the development
of the nanocomputer itself.

Devices made using molecular nanotechnology will contain many
orders of magnitude more parts than conventional devices, and
thus bring unparalleled problems of how these devices are to be
designed. To address this problem, J. Storrs Hall,
moderator of the sci.nanotech newsgroup, proposed a new approach
to automated design ("Combining
Agoric and Genetic Methods in Stochastic Design"). He
used genetic algorithms (GA) to create a random set of agents
("firms") that buy and sell designs in a simulated
market. The profit produced by each firm is fed back into the GA
as a fitness function to determine the fate of that firm. Hall
demonstrated that, if the language to define the search space is
well chosen, this combination of market and genetic methods will
produce correct answers to certain simple problems.

Computational Exploration of the Molecular World

Two speakers presented virtual reality systems for the
exploration of nanosystems. Creon Levit of NASA
Ames Research Center described a force feedback arm coupled not
to a real AFM tip, but instead to a simulation using the Brenner
Reactive Bond Order Molecular Dynamics Potential ("Virtual
Mechanosynthesis"). One use proposed for this system is
as a debugging tool to check strategies for mechanosynthesis
prior to experimenting with a real (and expensive) AFM. Rick
Stevens of Argonne National Laboratory presented a
visualization system that would let users walk into, and be
surrounded by, simulations of the molecular world, which could be
used as the basis for collaborations across the Internet ("Using
Immersive Virtual Reality for Visualizing and Modeling of
Molecular Nanosystems"). They anticipate using petaflop
supercomputers supporting simulations of billions of atoms to
allow users to investigate local structures while maintaining the
global context of those structures.

Tahir Cagin of the California Institute of
Technology reported molecular dynamics simulations of planetary
gears and a neon pump designed by Drexler and Merkle ("Molecular
Mechanics and Molecular Dynamics Analysis of Drexler-Merkle Gears
and Neon Pump"). Computational limitations currently
require that the planetary gear be simulated at unrealistically
high rotations, where it proved to be unstable. A second
generation gear, redesigned by Drexler and Merkle to be more
stable did indeed perform better, although there was some
slippage of gear teeth during rotation. Neon atoms were indeed
moved along the rotor of the pump as designed, although the rotor
deformed at certain rotational frequencies.

Toshishige Yamada of NASA Ames Research
Center presented calculations of the changes in energy bands of
one dimensional chains of silicon or magnesium atoms that could
be accomplished by placing selected dopant atoms at specific
places beside the chain such that the chains were predicted to
become semiconductors ("Doping
Scheme of Semiconduct-ing Atomic Chain").

Odds and Ends

One of the most ambitious ultimate applications of molecular
nanotechnology, originally proposed in Chapter 9 of Engines of
Creation, is the repair of damage induced during
cryogenic biostasis. Gregory Fahy of the Naval
Medical Research Institute reviewed the types of damage that
occurs to cells and to large organs during freezing, and the
strategies used to minimize such damage ("Cryopreservation
of Large Biological Systems"). The most promising
approach so far appears to be vitrification, the formation of a
quasi-stable glass without forming ice. The concentrations of
cryoprotective chemicals required for vitrification are toxic to
the cells, but recent experiments have shown that rabbit kidneys
treated with the chemicals, but not actually vitrified, can be
washed free of the chemicals and regain function. In terms of the
more important (for biostasis) issue of preserving brain
structure, current techniques preserve the neural connections
within large areas of dog brains, but there are always some areas
that look bad since it is not yet possible to completely prevent
ice crystal formation.

Foresight
Five: Wake Up and Smell the
Nanotubes

by Chris Worth

If you want to get ahead, get a beard. The wow-factor of any
science paper tends to be in direct proportion to the length of
facial hair on the paper's author, so when you saw whole rows at
the Foresight conference filled with ZZ Top lookalikes you knew
you were in for a treat.

And boy, did you get one. The talks49 over three days,
plus a bundle of posters salted with amusing
flakinessstretched minds like taffy, blocking your nose and
tightening your throat with the awesome potential of molecular
nanotechnology. Every day, the message became clearer: we're so
close you can taste the carbon.

And nanoelectronics, it seems, will come first. Smalley's
molecular wires burst from Nature covers and J.C.
Ellenbogen brought molecular transistors to life; P. Collins
found electronic devices tantalizingly patterned into carbon
nanotubes and sim after sim showed how tough they are. But
mechanosynthesis wasn't ignored: Michelson
of Zyvex approached the problem of cutting 3D parts out of a
surface and (with shades of Unbounding the
Future) thirty-foot high nanomachines dwarfed users of
startling new immersive GUIs.

It was fullerenes, however, that shed the most blood. Carbon
nanotubes were burnt, boiled, buckled and bent eight ways from
Sunday into a mass of graphs and figures all pointing towards
MNT's viability. The "Society for the Prevention of Cruelty
to Nanotubes" that came to life on the notice board won't
get many members when the sims look this cool.

Nanotechnologists are an articulate bunch. All papers were
given in plain talk, from the dense math of bonding energies to
the terminology-saturated world of molecular biology. It was good
to see the distances between disciplines shrink. And the moment I
can squash my brain back inside my skull, I'll sign up for next year.

Photos
from the Conference

Panel Session

Panelists (left to right) Rick Smalley, Ned Seeman, Ralph
Merkle, Bill Goddard and Jim Gimzewski field questions from
the floor in a wrap-up discussion at the close of the
Thursday session, in which Track One and Track Two were
combined.